Strong, tough, fatigue-resistant and 3D-printable hydrogel composites reinforced by aramid nanofibers

Three-dimensional (3D)-printable hydrogels exhibit a large elongation-at-break but low strength and modulus and poor fatigue resistance, restricting their applications in artificial tissue. Here, we synthesized 3D-printable hydrogel composites reinforced by aramid nanofibers (ANFs) by introducing ANFs into a hydrogel solution and then applying ultraviolet irradiation to this solution. Compared with those of the pure hydrogel, the strength, fracture energy and fatigue threshold of the 0.3 wt% ANF-hydrogel composite were simultaneously improved by about 10 times, and the modulus was improved by about 30 times, without a significant reduction in the elongation-at-break. The improvements in the modulus, strength and fatigue threshold of the composites were related to the formation of hybrid polymer networks, while the enhanced fracture energy were mainly attributed to chain entanglement, hydrogen bonding and phase separation. Owing to a high 3D-printing resolution and good biocompatibility, these ANF-hydrogel composites have potential applications in flexible electronic devices in organisms. The current study provides a universal and effective strategy for improving the mechanical properties of 3D-printable hydrogels.